1. Field of the Invention
This invention relates to a motor driven camera whose various operations are performed by motors as the drive sources.
2. Description of the Related Art
In the past, springs were used for driving the swinging motion of the movable mirror incorporated in the camera, constituting a quick-return mechanism together with other means. Of these, the electromagnet when actuated releases the mirror from the mechanical latch to effect swinging from the finder-viewing position to the exposure-retracted position by the force of the charged drive spring which overcomes the force of the return spring urging the mirror to move backward from the exposure-retracted position to the finder-viewing position. And, to charge the drive spring, the driving power of an electric motor for moving the windup transmission system was used in common. In the camera of this kind, therefore, as the motor alone was not sufficient, the expensive electromagnet structure had to be used for the purpose of actuating the movable mirror. Further, the load on the windup motor was increased. Hence there were problems that the cost was high and the speed of charging movement (including the winding up) was slow.
As a conventional example of the improved one, direct drive connection of the motor to the movable mirror was proposed (by Minolta Co. in its single-lens reflex camera named "Minolta 7000") with an advantage that the expensive electromagnet or actuator for the movable mirror could be removed. However, this proposal made use of an alternative mechanism in the form of a planetary clutch responsive to normal rotation of the windup motor for causing the movable mirror to flip upward to the exposure retracted position, and responsive to reversed rotation of that motor for driving the windup transmission system and the charge mechanism for the shutter. The use of such a switching mechanism produced problems that the minimum interval time between the successive two shots was increased, and, the life-time of the motor was shortened due to the overwork of the motor. In turn, therefore, many new problems arose that much desired increase of the framing rate for continuous shooting could not be achieved in any way, and that, to hold the movable mirror in the exposure retracted position, an additional mechanism of complicated structure was necessitated. Another feature of this improved proposal is that the rewinding is operated by using the common motor of the above-described windup, mirror drive and shutter charge mechanism. In actual practice, a rewind control button was manually sliden to operate another clutch of the thrust type, thereby the output shaft of the motor was brought into meshing engagement with the rewind transmission system. This feature was associated with a problem on manageability that, because the force necessary to move the thrust clutch was very strong, automatic transition from the windup to the rewind mode (or auto-rewind) was impossible to perform.
Attempts have been made to increase the framing rate by using three motors, of which the first is to charge both the drive spring for the mirror and the shutter, the second is to wind up film, and the third is to rewind the film, as disclosed in U.S. Pat. No. 4,616,913 corresponding to Japanese Laid-Open patent application No. Sho 61-183628 (and many others). In this patent, however, because of its using the conventional electromagnet structure for actuating the movable mirror, the problem of the high cost is not solved. Yet, this patent admits for a very high efficiency of transmission, since each mode is operated by the respective individual motor. If the damages resulting from the increase of the number of used motors of the cost and the space efficiency are limited to an acceptable minimum, it can be said that such a prior art is nearly ideal. In reality, on the other hand, for cameras to be developed year by year, the requirement of increasing the number of capabilities, heightening the grade of performance and advancing automation and the requirement of minimizing the bulk and size and lowering the production cost are becoming more desirable to fulfill at a time, although they are contradictory to each other in principle. After all, minimization of the size of the camera and reduction of the cost are becoming a problem that cannot be averted.
Also, in the camera having the motorized windup and rewind modes, when changing over from the windup to the rewind mode, the control mechanism therefor must operate in such a manner that, in the general case, the windup motor is taken out of drive connection with the windup side gear, and the takeup spool and the drive sprocket are freed, while simultaneously bringing the rewind motor into drive connection with the rewind fork which has so far been free.
This control mechanism may be actuated either manually from the outside of the camera by means of the slide knob or the rewind control button as in the cameras of, for example, U.S. Pat. Nos. 4,693,578 and 4,611,896, or automatically by means of the plunger or planetary gear mechanism as in the cameras of, for example, U.S. Pat. Nos. 4,548,304 and 4,752,793 .
The camera which is made necessary to actuate from the outside of its housing has a buzzer or an external display informing the user of when the last one of the prescribed number of film frames is shot, for he switches the camera to the rewind mode. Looking at this alarm display, the user will manipulate the knob or the like to operate the clutch or mode changeover mechanism. Thereupon, the camera starts to energize the rewind motor. Thus, the rewinding operation is started.
Differing from this, the camera which does not necessitate the manipulation of the external member or capable of automatically switching to the rewind mode has its plunger or planetary gear made to perform disengagement followed by engagement automatically, when the film is stretched as the number of fed film frame has reached the prescribed value. Thus, the rewinding operation is automatically started.
In comparison of the above-described two conventional examples, the latter camera that does not necessitate the awareness of the user to render operative the automatic rewind mechanism is more convenient. But it has such a drawback as follows. Since the completion of exposure of all the prescribed number of film frames is immediately followed by the automatic transit to the rewind mode, because the rewinding noise travels over a long distance in a quiet place, if, as the photographer is taking continuous shooting, it happens in, for example, a theater, he will be ashamed of annoying the audience around him. Also, in wild animal photography, as the rewinding noise frightens a bird or animal away, the photographer will fail to hold the chance of shooting it for the next film cartridge.
In the case of the former camera, on the other hand, though the inconvenience of the user manipulating the rewind control member is left unremedied, there is a merit that the user can make a decision on whether to do the rewinding or to abandon it at the given time. Hence, the above-described problem can be avoided.
Also, a camera having the automatic rewind mechanism is disclosed in U.S. Pat. No. 4,616,913. The winding up and rewinding of the film are operated by respective individual motors so that the only way for achieving automatic switching from the windup to the rewind mode is to control current supply to these motors. Moreover, the use of this type in the design of a motor driven camera provides a possibility of remarkably improving the efficiency of transmission of every drive connection.
However, in the camera disclosed in the above-cited patent, even after the camera has been switched to the rewind mode, the windup motor is left engaged with the windup transmission system. The load on the rewind motor is very heavy.
In connection with the above-cited U.S. Pat. No. 4,616,913, it should be pointed out that an embodiment is disclosed where use is made of a planetary clutch positioned in between the rewind motor and the rewind transmission system, and arranged to be cut out when the rewinding of the film is completed. For this purpose, the rotation of the rewind motor is reversed in response to detection of that completion, and then stopped after some reverse rotation.